The present invention relates in general to a piston for a fluid machine that includes a piston body made of resin and a coupler made of metal, and more particularly to a method for manufacturing the piston used in the fluid machine.
As a typical piston for the fluid machine, Japanese Unexamined Patent Publication No. 9-256952 is known. In the publication, a rotation restricting portion is formed on the piston in order to restrict the rotation of the piston around the axis of the piston that is accommodated in a cylinder bore of a compressor.
The rotation restricting portion is formed on a coupler (or a neck portion of the piston) that operatively connects the piston to a mechanism for driving the piston. The rotation of the piston is restricted by the contact of the rotation restricting portion against a housing of the compressor. The restriction of the rotation substantially prevents the coupler from contacting the piston driving mechanism. Thereby, vibration and noise to be generated due to the contact are prevented. In general, a coating is applied to the surface of the rotation restricting portion in order to reduce the sliding resistance between the rotation restricting portion and the housing.
As a typical piston for a fluid machine where a coating is applied, Japanese Unexamined Patent Publication No. 2000-274366 is known. In the publication, a piston body that is accommodated in a cylinder bore is made of resin in order to reduce the weight of the piston and reduce the sliding resistance between the piston body and the cylinder bore.
In the constitution, the piston body is fixed to the coupler that operatively connects the piston to a mechanism for driving the piston by an insert molding.
In the constitution according to Japanese Unexamined Patent Publication No. 2000-274366, however, reduction of a sliding resistance between a rotation restricting portion and the housing is not considered. In order to provide a means for reducing the sliding resistance between the rotation restricting portion and the housing, it is required to provide the means in a process other than the process for fixing the piston body to the coupler. That is, since a process for coating the piston body is omitted by employing the piston body made of resin, in a sense a cost is lowered. However, since the rotation restricting portion is formed in another process, it is actually hard to lower the cost by reducing the number of processes for manufacturing the piston. In addition, in this case, even if resin is employed as the means for reducing the sliding resistance, material of the resin is not considered. Therefore, even in an aspect of handling the material, the cost is not lowered.
The present invention is directed to a piston for a fluid machine, which lowers cost and a sliding resistance between the piston and a housing, and to a method for manufacturing the piston.
According to the present invention, a piston is used for a fluid machine. The fluid machine has a cylinder bore and a piston driving unit for driving the piston in a housing. The piston has a piston body made of resin, a coupler made of metal and a resin unit. The piston body is accommodated in the cylinder bore. The coupler is connected to the piston body. The coupler is operatively connected to the piston driving unit. The resin unit is connected to the coupler for preventing the coupler from contacting a contacting portion on the side of the housing. The piston body and the resin unit are made of the same resin.
Furthermore, the present invention has a following feature. A piston is used for a fluid machine. The fluid machine has a cylinder bore and a piston driving unit for driving the piston in a housing. The piston has a piston body made of resin, a coupler made of metal and a resin unit. The piston body is accommodated in the cylinder bore. The coupler is connected to the piston body while operatively connected to the piston driving unit. The resin unit is connected to the coupler for preventing the coupler from contacting a contacting portion of the housing. A method of manufacturing the piston includes the following step. The step is forming the resin unit and the piston body simultaneously in a process of forming the coupler by an insert molding.